Many robotic mechanisms require rotational motion for degrees of freedom. Depending upon the application, such degrees of freedom can require high ranges of motion (greater than +/−70 degrees). Industrial robots are capable of achieving high ranges of motion, and often utilize electric motors or hydraulic actuators with gear mechanisms to achieve the desired range of motion. Many robots, however, also require a compact form factor, low stiction and backlash, and lightweight structures that can support external structural forces, often leading designers of such robots to employ other power sources such as hydraulics or pneumatics. Some robots, for example, include anthropomorphic features to represent or mimic, for example, a human arm or leg. Human arms and legs have rotational degrees of freedom, such as humeral rotation, wrist rotation, thigh rotation, and calf rotation. Rotary actuators can be inherently rotational or can utilize a linear actuator with a mechanical mechanism. Typical approaches include the use of single and double vane rotary actuators, linear actuators using a simple crank, a bell crank, or “back hoe bucket” type linkages, and pulley and tendon mechanisms. Other methods such as rack and pinion methods, displacement gear motors, radial pistons driving a crank, and helical twister actuators have also been used.
Reference will now be made to the exemplary embodiments illustrated, and specific language will be used herein to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended.